Safety Assessment of Alkyl Taurate Amides and Taurate Salts as Used in Cosmetics Status: Final Report Release Date: February 8, 2016 Panel Meeting Date: December 14-15, 2015 The 2015 Cosmetic Ingredient Review Expert Panel members are: Chair, Wilma F. Bergfeld, M.D., F.A.C.P.; Donald V. Belsito, M.D.; Ronald A. Hill, Ph.D.; Curtis D. Klaassen, Ph.D.; Daniel C. Liebler, Ph.D.; James G. Marks, Jr., M.D.; Ronald C. Shank, Ph.D.; Thomas J. Slaga, Ph.D.; and Paul W. Snyder, D.V.M., Ph.D. The CIR Director is Lillian J. Gill, D.P.A. This report was prepared by Lillian C. Becker, Scientific Analyst/Writer. © Cosmetic Ingredient Review 1620 L Street, NW, Suite 1200 Washington, DC 20036-4702 ph 202.331.0651 fax 202.331.0088 [email protected] ABSTRACT This is a review of the safety of 20 alkyl taurate amides and taurate salts as used in cosmetics. The alkyl taurate amides and taurate salts in this report are all structurally related by having the same taurate (2-aminoethane-1-sulfonate) core. These ingredients mostly function in cosmetics as surfactants-cleansing agent. The Cosmetic Ingredient Review (CIR) Expert Panel (Panel) reviewed relevant data related to these ingredients. The Panel concluded that the alkyl taurate amides and taurate salts in this safety assessment are safe in cosmetics in the present practices of use and concentration described in this safety assessment when formulated to be non-irritating. INTRODUCTION This is a review of the scientific literature and unpublished data relevant to assessing the safety of alkyl taurate amides and taurate salts as used in cosmetics. The alkyl taurate amides and taurate salts in this report are all structurally related by having the same taurate (2-aminoethane-1-sulfonate) core. While the free acid, taurine, is a cosmetic ingredient, it is not included because it functions exclusively as a fragrance, which is within the purview of the Research Institute for Fragrance Materials (RIFM). According to the International Cosmetic Ingredient Dictionary and Handbook, these 20 ingredients mostly function in cosmetics as surfactants-cleansing agent (Table 1).1 The ingredients in this report are: • Potassium Taurate • Sodium Lauroyl Taurate • Sodium Methyltaurate • Sodium Methyl Lauroyl Taurate • Sodium Taurate • Sodium Methyl Myristoyl Taurate • Calcium Lauroyl Taurate • Sodium Methyl Oleoyl Taurate • Magnesium Methyl Cocoyl Taurate • Sodium Methyl Palmitoyl Taurate • Potassium Cocoyl Taurate • Sodium Methyl Stearoyl Taurate • Potassium Methyl Cocoyl Taurate • Sodium Methyltaurate Isopalmitamide • Sodium Caproyl Methyltaurate • Sodium Methyltaurine Cocoyl • Sodium Cocoyl Taurate Methyltaurate • Sodium Methyl Cocoyl Taurate • Sodium Taurine Cocoyl Methyltaurate • Sodium n-Isostearoyl Methyltaurate The Panel has previously concluded that many of the individual fatty acids that are residue components of the alkyl taurate amides are safe as used in cosmetics.2-10 The safety of these fatty acids may be relevant to the safety of the alkyl taurate amides (e.g., as residual manufacturing impurities, metabolic products of dermal amidases); the available data are well-documented in the existing CIR reports that can be found on the CIR website (http://www.cir-safety.org/ingredients) and will not be summarized here. The cocoyl moieties are derived from the constituent fatty acids of coconut acid, which is composed largely of various amounts of caproic acid, caprylic acid, capric acid, lauric acid, linoleic acid, myristic acid, oleic acid, palmitoleic acid, and stearic acid. The Panel has reviewed coconut acid, lauric acid, myristic acid, and oleic acid and concluded that these ingredients are safe as used. 2-10 Linoleic acid has not been reviewed by the Panel. Background information is provided on taurine, which is the starting material and a potential impurity in the manufacture of these ingredients. However, extensive toxicity information for taurine is not included because taurine is physiologically ubiquitous and present in relatively high concentrations throughout members of the animal kingdom, 11 including humans. Pertinent data were discovered in the European Chemicals Agency (ECHA) database.12-17 This database provides summaries of information generated by industry, and it is those summary data that are presented in this safety assessment when referenced. CHEMISTRY Definition and Structure The alkyl taurate amides and taurate salts are structurally related because these ingredients have the same taurate core (Figure 1). These ingredients vary by N-substitution and by the counter-ion of the sulfonate functional group. The simple taurate salts, potassium taurate, sodium methyltaurate, and sodium taurate, also vary by N-substitution (hydrogen or methyl) and counter-ion (sodium or potassium). Figure 1. The simple taurate salts (wherein R is hydrogen or methyl). The remaining ingredients in this report bear a fatty acyl N-substitution that forms, together with taurate, an amide (i.e., alkyl taurate amide; Figure 2). The alkyl taurate amides share a taurate core, and vary by fatty chain length and counter- ion. Some of the ingredients in this report have names that suggest discrete fatty chain-lengths; however, all of these ingredients, regardless of the nomenclature, are likely to be mixtures of substances with different chain lengths. The length specified in the names of each of these ingredients indicates the primary, or average, chain length of the substances in the mixture obtained through the batch separation and purification procedure employed. For example, those ingredients with a “cocoyl” name are the result of reaction with coconut acid, which has a known composition of approximately: 0-1% caproic, 5%-9% caprylic, 6%-10% capric, 44%-52% lauric, 13%-19% myristic, 0-1% palmitoleic, 1%-3% stearic, 5%-8% oleic, and trace-2.5% linoleic acid.7 Accordingly, not only do these alkyl taurate amides share the same taurate core and similar fatty chain lengths, but many of these ingredients have identical component overlap (e.g., there is likely some sodium methyl lauroyl taurate in sodium methyl cocoyl taurate and in sodium methyl myristoyl taurate (“myristoyl” likely has some smaller [lauroyl] and longer [palmitoyl] chain lengths therein). Figure 2. Sodium Caproyl Methyltaurate – an alkyl taurate amide. Furthermore, the composition of ingredients with plant source-derived acyl compounds such as sodium methyl cocoyl taurate, can be expected to vary from batch to batch and alternative vendors, because the acid starting material, coconut fatty acid, has a high carbon chain-length variability, dependent on factors such as growth conditions.18-24 As an illustrative example, the reported ranges of the components of sodium methyl cocoyl taurate are presented in Table 2. Physical and Chemical Properties Most of the alkyl taurate amides are solids (Table 3). For example, calcium lauroyl taurate is a white powder with a high fluidity.25 One commercial supplier reports that the particle size of their calcium lauroyl taurate is 8 µm and that the particles 25 have a plate-like shape. The particle size distribution reported by a supplier of sodium methyl cocoyl taurate was: D10 (the diameter at which 10% of a sample’s mass is comprised of smaller particles) = 3.87±0.16 µm; D50 (the diameter at which 50% of a sample’s mass is comprised of smaller particles) =16.58±0.67 µm; and D90 (the diameter at which 90% of a sample’s mass is comprised of smaller particles) = 59.97±4.58 µm.17 TAURINE Taurine is a white or colorless crystal powder.26 It has high water solubility and is very hydrophilic because of its zwitterionic form, both in solids and in solution. Method of Manufacture ALKYL TAURATE AMIDES In general, alkyl taurate amides may be manufactured by reaction of taurine, N-methyltaurine, or a taurate salt, with the appropriate fatty acid. For example, manufacture of sodium methyl stearoyl taurate may be accomplished by heating triple-pressed stearic acid, sodium methyltaurate solution, and boric acid to 200˚C while stirring with a subsurface nitrogen purge, distilling off any water.27 The stirring continues at 195-200˚C for 6 h at atmospheric pressure and then for 3 h at 100 mm Hg vacuum. The mass is cooled and the resulting product, an off-white waxy solid, is ground to a powder. The product is reported to be 64.0% sodium methyl stearoyl taurate as active ingredient, 29.5% free fatty acid, 2.5% sodium N-methyltaurate, and 4.0% other unspecified chemicals. The conversion of sodium methyltaurate using this method was reported to be greater than 91%. Using coconut fatty acid in place of the triple-pressed stearic acid resulted in a conversion of 97%. In another process, calcium lauroyl taurate was reported to be synthesized by dissolving taurine in a mixture of deionized water and isopropyl alcohol (86:14, wt/wt) followed by the addition of sodium hydrate. Lauric acid chloride and 48% aqueous sodium hydrate solution is dropped into the taurine solution for 1 h at 40˚C followed by stirring for 1 h at the same temperature to produce sodium lauroyl taurate. Hydrochloric acid (35%) and an aqueous calcium chloride solution (20%) are added, and the reaction mixture stirred for 1h at 40˚C. The white precipitate is filtered and the cake washed with deionized water and isopropyl alcohol, then dried.27 Sodium methyl cocoyl taurate is reported to be manufactured and sold as a mixture with sodium chloride and water, with active ingredient ranging from 24.0%-33%.19-24 TAURATE SALTS Taurine may be produced by a cyclic process of reacting ethylene oxide with sodium bisulfite and ammonium to obtain sodium taurate.28 Excess ammonia is removed from the reaction mixture, and the sodium taurate is neutralized with sulfur dioxide or sulfurous acid to recover taurine. Sodium bisulfate is regenerated and is then reacted with ethylene oxide. The salt forms can then by synthesized by simply reacting with the appropriate base, such as sodium hydroxide.